In general, Al and Al alloys are used for a reflecting film used for optical recording media such as CD (compact disc), DVD (digital versatile disc) and the like and a light-reflective conductive film used for displays such as a reflection type STN (super twist nematic) liquid crystal display, an organic EL (electro luminescence) display and the like.
A light-reflective thin film used for uses such as the optical recording media, the liquid crystal display and the organic EL display each described above is usually produced by preparing a sputtering target material having a desired quality and forming a film using this sputtering target material by an RF (radio frequency) sputtering method and a DC (direct current) sputtering method.
The thin films comprising Al and Al alloys which are produced by the methods described above have a reflectance of some extent and a low electric resistance and forms a passive coating film on a surface, so that it has a stable corrosion resistance as well in the air. However, the thin films comprising Al and Al alloys have a reflectance of about 80% in the case of, for example, light having a wavelength of 700 nm, and it is not sufficiently satisfactory to uses in which the high reflectance is required.
Accordingly, it is proposed to use Au and Ag as a sputtering target material in place of Al and Al alloys for optical disc media represented by, for example, CD-R and DVD to form a thin film. Further, it is proposed to use Ag having a high reflectance as a thin film material as well for a reflection type STN liquid crystal display.
However, Au is expensive, and Ag has problems on a corrosion resistance, particularly a halogen resistance (Cl and others), an acid resistance and a sulfurization resistance as compared with Al. For example, if Ag is reacted with a halogen element such as Cl, it is discolored and reduced in a reflectance, and if Ag is reacted with sulfur and oxygen, a sulfide and an oxide of Ag are formed to blacken the film and reduce a reflectance thereof.
Thus, it is proposed to elevate a corrosion resistance (a halogen resistance, an acid resistance and a sulfurization resistance) by adding a small amount of Mg to Ag to turn them into an alloy in Japanese Patent Application Laid-Open No. 3363/1995 and by adding a small amount of Pd to Ag to turn them into an alloy in Japanese Patent Application Laid-Open No.109943/2000. Further, an AgAu alloy improved in recording sensitivity and a C/N ratio by adding 5 to 50 at % of Au to Ag is disclosed in Japanese Patent Application Laid-Open No. 156753/1991.
However, a satisfactory corrosion resistance of Ag is not obtained by these Ag alloys, and still present is the problem that the corrosion resistance, particularly the halogen (Cl and the like) resistance is elevated to some extent but the sulfurization resistance is not so different from that of Ag, so that the satisfactory corrosion resistance is not obtained.
An object of the present invention is to provide a sputtering target material for forming a thin film, comprising an Ag alloy which is improved in a corrosion resistance, particularly a halogen resistance, an acid resistance and a sulfurization resistance while maintaining a high reflectance and a thin film formed using the above sputtering target material.